JP7367759B2 - Electrical insulating resin composition and electrical insulator - Google Patents

Description

The present disclosure relates to an electrical insulating resin composition capable of forming an electrical insulator having excellent withstand voltage life characteristics against surge voltages, and an electrical insulator using the electrical insulating resin composition.

BACKGROUND ART In recent years, inverter-controlled electrical equipment has been widely used in various fields from the viewpoint of energy saving and variable speed control. In particular, control systems in the fields of hybrid vehicles and industrial motors are required to be highly efficient. Therefore, inverter drives are being applied as variable speed devices, and devices are rapidly becoming smaller, lighter, more heat resistant, and driven at higher voltages.

2. Description of the Related Art In recent years, as inverter-driven power devices, high-speed switching elements such as IGBTs (Insulated Gate Bipolar Transistors) have been developed. On the other hand, as the surge voltage value increases due to high-speed switching of power devices, the frequency of cases where motors and electrical equipment quickly break down and have extremely shortened lifespans is increasing.

It has been pointed out that one of the causes of the above-mentioned dielectric breakdown is that partial discharge occurs when a high voltage is applied to a motor coil or the like due to a surge, and the insulation film of the electrical insulator deteriorates. Therefore, in order to extend the lifespan of motors and electrical equipment driven by inverters, there is a need for electrical insulating materials that can suppress deterioration of insulation coatings due to partial discharge.

On the other hand, polyamide-imide resins are used in various applications as important electrical insulating materials because of their excellent processing resistance, heat resistance, chemical resistance, hydrolysis resistance, and the like. Particularly in the field of automotive motors (including hybrid vehicle motors), during the winding process during motor manufacturing, the windings are subjected to stretching, bending, wear, etc. while being subjected to strong tension. . Therefore, the winding wire is required to have excellent processing resistance such as flexibility.

Also, the windings are often installed in the presence of transmission oil. Therefore, performance requirements for the windings used in motors include that they should not be attacked by transmission oil and that they should be resistant to hydrolysis due to moisture in the oil. Furthermore, the winding wire is required to have heat resistance that allows it to withstand use at high temperatures. From this point of view, polyamide-imide resin has become indispensable as an electrical insulating material used in windings (particularly insulated wires).

From these viewpoints, it is possible to suppress destructive deterioration of the insulating film due to partial discharge (hereinafter also referred to as partial discharge deterioration), and to improve machining resistance, heat resistance, chemical resistance, hydrolysis resistance, etc. Various studies are being conducted toward the realization of electrical insulating materials that meet typical performance requirements for insulated wires.

For example, a resin composition containing a polyamideimide resin modified with a specific polybutadiene resin has been disclosed as an electrical insulating material capable of suppressing partial discharge deterioration (Patent Document 1). Further, as other electrical insulating materials, resin compositions containing a resin such as polyamide-imide resin and inorganic particles such as silica have been disclosed (Patent Documents 2 to 4).

However, in response to the recent rise in surge voltage values, it is difficult to obtain sufficiently satisfactory withstand voltage life characteristics using conventional electrical insulating materials. Therefore, there is a demand for an electrical insulating material that has higher resistance to partial discharge deterioration than conventional materials and can improve the withstand voltage life characteristics.

JP 2015-84329 Publication Japanese Patent Application Publication No. 2001-307557 Japanese Patent Application Publication No. 2012-197367 Japanese Patent Application Publication No. 2008-251295

Inorganic particles are one way to increase the partial discharge deterioration resistance of an insulating film formed from an electrically insulating material containing a resin such as polyamide-imide resin and inorganic particles such as silica, and to improve the withstand voltage life of electrical insulators. One example is increasing the content of. However, when the content of inorganic particles in an electrically insulating material is increased, the flexibility, adhesion to a conductor, and dielectric breakdown voltage characteristics of the insulating film tend to decrease. When the flexibility and adhesion of an insulating film are low, the insulation properties of an insulated wire having such an insulating film are likely to decrease due to mechanical stress during winding. Furthermore, if the dielectric breakdown voltage characteristics are low, dielectric breakdown of the insulating film is likely to occur not only when partial discharge occurs. Furthermore, when the content of inorganic particles in the electrically insulating material is increased, the viscosity tends to increase and the storage stability tends to decrease.

For this reason, while maintaining the typical properties required for the insulation film of insulated wires, such as flexibility, adhesion, and dielectric breakdown voltage characteristics, compared to conventional electrical insulation materials containing inorganic particles, , it is desired to improve resistance to partial discharge deterioration, improve withstand voltage life characteristics, and improve storage stability.

Therefore, the present disclosure provides an electrically insulating resin composition that can form an insulating film that has excellent flexibility, adhesion, and dielectric breakdown voltage characteristics as well as resistance to partial discharge deterioration, and has excellent storage stability. provide something. Further, the present disclosure provides an electrical insulator with high insulation reliability using the electrically insulating resin composition.

The present inventors have conducted intensive studies on electrically insulating resin compositions containing polyamide-imide resin and inorganic particles. As a result, by using a specific amount of silica fine particles as inorganic particles, it is possible to maintain typical properties required for insulation coatings of insulated wires, such as flexibility, adhesion, and dielectric breakdown voltage characteristics, while at the same time The present inventors have discovered that it is possible to realize an electrically insulating resin composition that can enhance discharge deterioration resistance, improve withstand voltage life characteristics, and have excellent storage stability, and have completed the present invention. That is, the present invention relates to the embodiments described below. However, the present invention is not limited to the following embodiments.

One embodiment relates to an electrically insulating resin composition containing a polyamide-imide resin and fine silica particles, in which the content of fine silica particles is 6 to 24% by mass based on the total mass of solid content. The silica fine particles preferably include wet silica fine particles. The turbidity of the electrically insulating resin composition is preferably 30 NTU or less.

One embodiment relates to an electrical insulator having a conductor and an insulating film formed using the electrically insulating resin composition of the above embodiment. Preferably, the conductor is a metal wire.

According to the present invention, an insulating film is formed that has excellent resistance to partial discharge deterioration in addition to the typical characteristics required for an insulating film of an insulated wire, such as flexibility, adhesion, and dielectric breakdown voltage characteristics. It is possible to provide an electrically insulating resin composition that is possible and has excellent storage stability. Moreover, an electrical insulator with high insulation reliability can be provided using the electrically insulating resin composition.

FIG. 1 is a schematic cross-sectional view showing one embodiment of an insulated wire. FIG. 2 is a schematic cross-sectional view showing another embodiment of the insulated wire. FIG. 3 is a schematic cross-sectional view showing another embodiment of the insulated wire. FIG. 4 is a schematic cross-sectional view showing another embodiment of the insulated wire.

Hereinafter, embodiments of the present invention will be described in more detail, but the present invention is not limited to the embodiments described below.

1. Electrical Insulating Resin Composition One embodiment relates to an electrically insulating resin composition containing a polyamide-imide resin and silica fine particles, wherein the content of the silica fine particles is 6 to 24% by mass based on the total mass of the solid content. . Each component will be explained below.

[Polyamideimide resin]
Polyamide-imide resin is a resin that has amide bonds and imide bonds in its molecules. Polyamide-imide resin is a monomer mixture containing an acid component containing tricarboxylic anhydride or its derivative (hereinafter also referred to as acid component (a)) and a diisocyanate compound or diamine compound (hereinafter also referred to as component (b)). It is a resin obtained by reaction. The electrically insulating resin composition may contain one type of polyamideimide resin, or may contain two or more types of polyamideimide resin.

(Acid component (a))
The tricarboxylic anhydride used as the acid component (a) may be any trivalent carboxylic acid having an acid anhydride group that reacts with the isocyanate group or amino group in the component (b). To produce the polyamideimide resin, tricarboxylic acid anhydrides or derivatives thereof can be used without particular restrictions.
From the viewpoint of heat resistance, the tricarboxylic acid anhydride in the acid component (a) preferably has a structure containing an aromatic group. In one embodiment, the acid component (a) preferably contains a tricarboxylic acid anhydride represented by the following formula (I) or the following formula (II). Among these, trimellitic anhydride is particularly preferred from the viewpoint of heat resistance and cost. The tricarboxylic acid anhydride represented by the following formula (I) or the following formula (II) may be used alone or in combination of two or more types depending on the purpose.

式中、Ｘ^１は、－ＣＨ_２－、－ＣＯ－、－ＳＯ_２－又は－Ｏ－を示す。

In the formula, X ¹ represents -CH ₂ -, -CO-, -SO ₂ - or -O-.

In other embodiments, the acid component (a) may further include an acid component different from the tricarboxylic anhydride. For example, as part of the acid component (a), a tetracarboxylic dianhydride may be further included, if necessary. Specific examples of tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic acid. Dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4'-sulfonyldiphthalic dianhydride, m-terphenyl-3,3',4,4'-tetracarboxylic dianhydride Anhydride (3,3'',4,4''-m-terphenyltetracarboxylic dianhydride), 4,4'-oxydiphthalic dianhydride, 1,1,1,3,3,3- Hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride , 2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis [4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldi Siloxane dianhydride, butanetetracarboxylic dianhydride, bicyclo-[2,2,2]-oct-7-ene-2:3:5:6-tetracarboxylic dianhydride, etc. can be used. .

(Component (b))
The diisocyanate compound or diamine compound is not particularly limited, and any compound having two isocyanate groups or amino groups in the molecule may be used. In one embodiment, component (b) preferably contains an aromatic compound having an isocyanate group or an amino group represented by the following formulas (III), (IV), and (V).

In the above formula, R ¹ and R ² each independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a hydroxyl group. The alkyl group or alkoxy group preferably has 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, and even more preferably 1 to 10 carbon atoms. In the alkyl group or alkoxy group, at least one hydrogen atom may be substituted with a halogen atom such as a fluorine atom. In one embodiment, R ¹ and R ² are preferably each independently a hydrogen atom.
Y represents an isocyanate group or an amino group, respectively.
X ² represents -CH ₂ -, -C(=O)-, -S(=O)-, -SO ₂ -, -O-, -S-, or -CR ³ R ⁴ -. R ³ and R ⁴ each independently represent the above alkyl group or alkoxy group. The alkyl group or alkoxy group is as described above. In one embodiment, R ³ and R ⁴ are one or more substituents selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a trifluoromethyl group, a trichloromethyl group, and a phenyl group. In one embodiment, X ² is preferably -CH ₂ -.

Specific examples of the aromatic diisocyanate compound or aromatic diamine compound represented by the above formula (III), (IV) or (V) include 4,4'-diisocyanatodiphenylmethane, 4,4'-diisocyanatobiphenyl, 3,3'-diisocyanatobiphenyl, 3,4'-diisocyanatobiphenyl, 4,4'-diisocyanato-3,3'-dimethylbiphenyl, 4,4'-diisocyanato-2,2'-dimethylbiphenyl, 4,4'-diisocyanato-3,3'-diethylbiphenyl, 4,4'-diisocyanato-2,2'-diethylbiphenyl, 4,4'-diisocyanato-3,3'-dimethoxybiphenyl, 4,4'- Diisocyanato-2,2'-dimethoxybiphenyl, 1,5-diisocyanatonaphthalene, 2,6-diisocyanatonaphthalene, 4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-diamino Biphenyl, 3,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3 '-diethylbiphenyl, 4,4'-diamino-2,2'-diethylbiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 4,4'-diamino-2,2'-dimethoxybiphenyl, Examples include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene. These may be used alone or in combination of two or more.

In addition, examples of the diisocyanate compound or diamine compound include tolylene diisocyanate, xylylene diisocyanate, 4,4'-diisocyanatodiphenyl ether, 2,2-bis[4-(4'-isocyanatophenoxy)phenyl]propane, Aromatic diisocyanate compounds or aromatic diamine compounds such as tolylene diamine, xylylene diamine, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4'-aminophenoxy)phenyl]propane can be used. can.

Further, as the diisocyanate compound or diamine compound, for example, hexamethylene diamine, 2,2,4-trimethylhexamethylene diamine, diaminoisophorone, bis(4-aminocyclohexyl)methane, 1,4-diaminotranscyclohexane, hydrogenated m -xylylene diamine, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, diisocyanatoisophorone, bis(4-isocyanatocyclohexyl)methane, 1,4-diisocyanatotranscyclohexane, hydrogenated m-xylylene Aliphatic or cycloaliphatic diisocyanate compounds such as diisocyanates or diamine compounds can be used. However, when using the above-mentioned aliphatic or alicyclic compound, it is preferable to use the above-mentioned aromatic diisocyanate compound or aromatic diamine compound together. The amount of the aliphatic or alicyclic compound used is preferably 50 mol% or less of the total amount of the diisocyanate compound or diamine compound from the viewpoint of heat resistance of the resulting resin.

The diisocyanate compound or diamine compound mentioned above can also be used in combination with a trifunctional or more functional polyisocyanate compound or polyamine compound.

In one embodiment, as the diisocyanate compound or diamine compound, 4,4'-diphenylmethane diisocyanate is particularly preferable in consideration of the balance of heat resistance, solubility, mechanical properties, cost, etc.

In addition, in order to avoid deterioration over time, if necessary, one in which the isocyanate groups are stabilized with a blocking agent may be used. Examples of the blocking agent include alcohol, phenol, oxime, etc., but there is no particular restriction.

(Blending ratio of acid component (a) and component (b))
When producing the polyamide-imide resin, the ratio of the amount of component (b) (representing the diisocyanate compound or diamine compound) to the acid component (a) (molar ratio of (b)/(a)) is particularly It can be adjusted without restriction. If the molar ratio becomes too small, it tends to be difficult to increase the molecular weight of the resin. On the other hand, if the molar ratio is too large, the foaming reaction will become more intense, more unreacted components will remain, and the stability of the resin will tend to deteriorate.

In one embodiment, the molar ratio of component (b) to 1 mole of acid component (a) is 0.6 to 1.4, since it is easy to obtain the desired Mn and acid value. It is preferably from 0.7 to 1.3, particularly preferably from 0.8 to 1.2. The molar ratio of the above compounding amount is the isocyanate group of the diisocyanate compound or diamine compound in component (b) to the total number of moles of carboxyl group and acid anhydride group in acid component (a), and optionally contained reactive hydroxyl group. and the total number of moles of amino groups.

Polyamideimide resin can be synthesized, for example, according to the following manufacturing method.
(1) A method in which acid component (a) and component (b) are mixed at once and reacted to synthesize a polyamide-imide resin.
(2) Acid component (a) is reacted with component (b) in excess amount to synthesize an amide-imide oligomer having an isocyanate group at the terminal, and then acid component (a) is added and reacted to form polyamide. How to synthesize imide resin.
(3) An excess amount of acid component (a) and component (b) are reacted to synthesize an amide-imide oligomer having an acid or acid anhydride group at the terminal, and then acid component (a) and component (b) are reacted. A method of synthesizing polyamideimide resin by adding and reacting.

(reaction temperature, reaction time)
In any of the above methods, the reaction temperature is preferably in the range of 80 to 150°C. Further, the reaction time is determined in consideration of obtaining the desired number average molecular weight (Mn), and is usually preferably 1 to 10 hours.

(Solvent during reaction)
The solvent (synthesis solvent) used during the synthesis of the polyamideimide resin is not particularly limited, but includes, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, γ-butyrolactone, N,N'-dimethylpropylene urea [ 1,3-dimethyl-3,4,5,6-tetrahydropyridimin-2(1H)-one], polar solvents such as dimethyl sulfoxide, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and sulfolane, xylene, and toluene. Examples include aromatic hydrocarbon solvents and ketones such as methyl ethyl ketone and methyl isobutyl ketone.

The amount of the synthetic solvent used is not particularly limited, but it is preferably 50 to 180 parts by mass, and 60 to 120 parts by mass, based on 100 parts by mass of the total amount of acid component (a) and component (b). It is more preferable that there be. When the amount of the synthesis solvent used is adjusted within the above range, it is possible to suppress the occurrence of a foaming reaction during synthesis, and it becomes easy to appropriately adjust the time required for synthesis.

(Molecular weight of polyamideimide resin)
Generally, the number average molecular weight (Mn) of polyamide-imide resin used as an electrical insulating material is preferably 5,000 or more, and preferably 10,000 or more, from the viewpoint of ensuring the strength of the coating film. More preferably, it is 12,000 or more. On the other hand, from the viewpoint of workability during painting, the Mn of the polyamide-imide resin is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less.

Although not particularly limited, in one embodiment, a polyamide-imide resin having an Mn of 12,000 to 30,000 can be suitably used to constitute the polyamide-imide resin composition. The Mn of the polyamideimide resin is more preferably 12,000 to 20,000. When a polyamideimide resin having Mn within the above range is used, it tends to be easier to improve the dispersibility of silica fine particles.

Mn of the polyamide-imide resin can be adjusted by adjusting the amount of raw materials charged, reaction time, etc. For example, it can be controlled by sampling during resin synthesis, measuring by gel permeation chromatography (GPC) using a standard polystyrene calibration curve, and continuing the reaction until the desired Mn is reached.

Further, in one embodiment, the polyamide-imide resin preferably has an acid value of 30 to 50 mgKOH/g. The acid value is more preferably 35 to 45 mgKOH/g. Here, the above acid value represents the number of milligrams (mg) of KOH required to neutralize 1 g of polyamide-imide resin, and the carboxyl group in the polyamide-imide resin is the ring-opened carboxyl group and acid anhydride group. The acid value is the sum of the

When a polyamide-imide resin having an acid value within the above range is used, the polyamide-imide resin tends to be easily dissolved or dispersed in the mixed solvent described below. Moreover, there is a tendency that gelation of the polyamide-imide resin composition finally obtained over time can be easily suppressed. Furthermore, although not bound by theory, it is thought that the dispersibility of the silica fine particles is improved due to the interaction between the carboxyl group in the polyamideimide resin and the silica fine particles described below.

(Silica fine particles)
Among typical inorganic particles used in electrically insulating materials, silica is preferred because it has excellent dispersibility in resin and particles are less likely to aggregate. In particular, it is preferable to use silica fine particles for polyamide-imide resin.
In this specification, "silica fine particles" means silica (silicon oxide) having an average primary particle diameter of 50 nm or less. Silica fine particles are expected to exhibit beneficial properties such as improved film formability and adhesion of an insulating film due to their small particle size.

In one embodiment, from the viewpoint of film formability and adhesion, the average primary particle diameter of the silica fine particles is preferably 40 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less. From the viewpoint of handleability, etc., the average primary particle diameter of the silica fine particles is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 7 nm or more, and most preferably 10 nm or more. In one embodiment, the average primary particle size of the silica fine particles may range from 10 nm to 20 nm, more preferably from 10 nm to 15 nm.

As used herein, the term "average primary particle diameter" refers to the average particle diameter of aggregated particles, that is, not the secondary particle diameter, but the average particle diameter of non-agglomerated particles. The average primary particle diameter of silica fine particles can typically be measured by a method using a laser diffraction particle size distribution analyzer or a transmission electron microscope (TEM). For example, in a method using TEM, first, the area of each particle image of at least 100 particles randomly selected from a composition or dispersion is measured using TEM. Next, the diameter of a circle having the same area as the obtained area value is regarded as the particle diameter, and the average value of each particle diameter is calculated by known statistical processing to obtain the average primary particle diameter.

From the viewpoint of increasing resistance to partial discharge deterioration, the content of silica fine particles in the electrically insulating resin composition is preferably 6% by mass or more, more preferably 8% by mass or more, and 10% by mass, based on the total mass of the solid content. The above is more preferable. On the other hand, from the viewpoint of obtaining excellent dispersibility, the content of silica fine particles in the electrically insulating resin composition is preferably 24% by mass or less, more preferably 22% by mass or less, and 20% by mass or less, based on the total mass of the solid content. It is more preferably less than % by mass.

In one embodiment, the content of silica fine particles in the electrically insulating resin composition is preferably in the range of 6 to 24% by mass, more preferably in the range of 8 to 20% by mass, based on the total mass of the solid content, and more preferably 10 to 24% by mass. A range of 18% by weight is more preferred, and 10-15% by weight is most preferred. As described below, when a sol of silica particles (silica sol) is used, the above content means a value calculated from the solid content of silica particles contained in the silica sol.

The use of silica particles is expected to exhibit beneficial properties such as improved film formability and adhesion of insulating coatings. However, on the other hand, in comparison with silica particles having an average primary particle diameter of more than 50 nm, silica fine particles tend to cause secondary aggregation and tend to have poor dispersibility. Therefore, when an electrically insulating resin composition is constructed using silica fine particles, the composition generally contains aggregates with non-uniform particle sizes, resulting in deterioration of properties such as cracking of the insulating film and the viscosity of the resin composition. It is thought that problems such as rising are likely to occur.

However, according to the electrical insulating resin composition of the above embodiment, by using a specific amount of silica fine particles, the withstand voltage life characteristics can be improved without deteriorating the properties of the insulating film, and the excellent Storage stability can also be obtained. Although not bound by theory, secondary aggregation is suppressed by using a specific amount of silica fine particles, and as a result, the silica fine particles are uniformly dispersed in the insulating resin composition while maintaining the primary particle size. It is presumed that this is because a good dispersion state is achieved and viscosity increase is suppressed.

The silica fine particles are not particularly limited except that the average primary particle diameter is 50 nm or less, and known silica fine particles can be used. Methods for synthesizing fine silica particles are broadly classified into dry methods and wet methods, but fine silica particles produced by either method may be used. Here, the dry method includes a combustion method and an arc method. In addition, the wet method includes a precipitation method, a gel method, and a sol-gel method.

In one embodiment, silica fine particles produced by a wet method (hereinafter referred to as wet silica fine particles) can be suitably used. Wet silica particles have more silanol groups on their surfaces than silica particles produced by a dry method (hereinafter referred to as dry silica particles). Therefore, when wet silica fine particles are used, there are advantages such as ease of surface treatment of the silica fine particles. In addition, when wet silica is used, its compatibility with the insulating resin is improved compared to dry silica, so excellent dispersibility can be easily obtained.

In one embodiment, among the wet silica particles, silica particles produced by a sol-gel method (hereinafter referred to as sol-gel silica particles) can be more preferably used. Sol-gel silica fine particles can typically be produced by using tetraalkoxysilane and performing hydrolysis and polycondensation with an ammonia catalyst in a solution.

As described above, in the electrically insulating resin composition of the above embodiment, by using a specific amount of silica fine particles, a decrease in dispersibility is suppressed, and an excellent withstand voltage life can be realized. The dispersibility of silica fine particles in an electrically insulating resin composition can be evaluated, for example, by turbidity measured according to a transmitted scattered light method.

In one embodiment, the turbidity of the electrically insulating resin composition having a solid content of 50% by mass or less, more preferably 40% by mass or less, even more preferably 20 to 40% by mass is preferably 30 NTU or less. The turbidity is more preferably 20 NTU or less, and even more preferably 10 NTU or less. The above-mentioned solid content means the ratio of the total amount of polyamide-imide resin and silica fine particles to the total mass of the electrically insulating resin composition. The unit of turbidity, NTU (Nephelometric Turbidity Units), means a nephelometric turbidity unit. Among silica particles, when using sol-gel silica particles manufactured by the sol-gel method, electrical insulation with a turbidity within the above range is used. A resin composition can be easily formed.

The storage stability of the electrically insulating resin composition can be evaluated by the rate of change in viscosity over time (%) of the polyamide-imide resin composition (varnish) before and after storage. In one embodiment, a certain amount of a polyamideimide resin composition having a solids content of 10 to 50% by mass was placed in a sealed container, and the sealed container was stored in a dryer set at 25° C. for one month. In this case, it is preferable that the viscosity change rate over time before and after storage is equal to or smaller than the viscosity change rate over time of a varnish that does not contain silica fine particles.

In one embodiment, the rate of change in viscosity over time of the varnish is preferably 24% or less. However, if the initial viscosity of the electrically insulating resin composition is too high, even if the above-mentioned rate of change in viscosity over time is small, if the initial viscosity is high, the handleability tends to be poor. Therefore, the initial viscosity (Pa·s) of the electrically insulating resin composition is preferably 2.3 or less, more preferably 2.1 or less, and even more preferably 2.0 or less. Therefore, it is more preferable that the varnish has an initial viscosity within the above range and a rate of change in viscosity over time of 24% or less. Among silica fine particles, when sol-gel silica fine particles produced by a sol-gel method are used, an electrically insulating resin composition (varnish) that is easy to handle and has excellent storage stability can be easily constructed.

The silica fine particles may be treated with a surface treatment agent such as a silane coupling agent or a dispersant from the viewpoint of improving dispersibility in the resin. Specific examples of the silane coupling agent include known alkoxy type silane coupling agents. Specific examples of the dispersant include known phosphate ester dispersants.

The silica fine particles may be used in the form of a silica sol, and may be subjected to solvent substitution. Here, the silica sol refers to a dispersion in which fine silica particles are dispersed in a dispersion medium, and has fluidity. In one embodiment, the silica microparticles are preferably used in the form of a silica sol. In general, silica particles with an average primary particle diameter of 50 nm or less are prone to secondary agglomeration, but when silica sol is used, it is easy to maintain good dispersibility and suppress particle sedimentation due to aggregation. It tends to be easy.

The dispersion medium in the silica sol preferably has excellent compatibility with the polyamideimide resin. As a dispersion medium, it is possible to use, for example, N,N-dimethylacetamide, methyl ethyl isobutyl ketone, water or methanol. In addition, a mixed solvent of xylene and butanol, etc. can also be used. Among these, silica sol containing N,N-dimethylacetamide as a dispersion medium can be suitably used. In one embodiment, the dispersion medium may be the same as the mixed solvent described below.

Silica sol may be a commercially available product, but it can also be prepared according to methods known to those skilled in the art. To produce silica sols, common methods of dispersing powders in liquids can be applied. Examples include a method in which fine silica particles, a dispersion medium, and other components such as a dispersant are mixed, and then a dispersion treatment is performed according to an ultrasonic method, a mixer method, a three-roll method, a ball mill method, or the like. Although not particularly limited, the amount of silica fine particles blended in the silica sol may be in the range of 10 to 50% by mass, more preferably in the range of 20 to 40% by mass, based on the total mass of the silica sol. good.

In one embodiment of the electrically insulating resin composition, the silica fine particles described above and other inorganic particles may be used in combination within a range that maintains excellent dispersibility. For example, the above silica fine particles and silica having an average primary particle diameter exceeding 50 nm may be used in combination. Inorganic particles other than silica that can be used in combination include metal oxides such as aluminum oxide (alumina), titanium oxide, magnesium oxide, and zirconium oxide. Other specific examples include clay, talc, barium sulfate, and calcium carbonate.

(Mixed solvent)
In one embodiment, the electrically insulating resin composition may include the polyamide-imide resin, the silica fine particles, and a solvent for mixing these components (hereinafter referred to as a mixed solvent). The mixed solvent is preferably one that can dissolve the polyamide-imide resin, and may be the same as the synthesis solvent used during the synthesis of the polyamide-imide resin. Therefore, in order to produce an electrically insulating resin composition, the reaction solution obtained during production of polyamideimide resin can also be used as it is. In one embodiment, the synthesis solvent and mixed solvent preferably include N-methyl-2-pyrrolidone and/or N,N-dimethylacetamide.

In the electrically insulating resin composition, the blending amount of the synthetic solvent and/or mixed solvent is not particularly limited. The polyamide-imide resin can be diluted with a synthetic solvent and/or a mixed solvent, and the blending amount can be adjusted so as to obtain a viscosity suitable for the desired use. In one embodiment, the electrically insulating resin composition may be in the form of an electrically insulating paint (varnish) containing a polyamideimide resin, silica fine particles, and a solvent. When preparing the electrically insulating resin composition as a varnish, the solid content is generally preferably 10 to 50% by mass, more preferably 20 to 40% by mass, based on the total mass of the varnish. By adjusting the solid content in the varnish to the above range, excellent coating properties can be obtained, and the coating can be repeated to easily form a thick film. The solid content may typically be the total amount of polyamideimide resin and silica fine particles.

(Other ingredients)
The electrically insulating resin composition may further contain additives such as colorants, if necessary. It is preferable to adjust the blending amount of the additive within a range that does not deteriorate the film properties.

The electrically insulating resin composition is prepared by mixing and dispersing the polyamide-imide resin, the silica fine particles, and, if necessary, other components such as a mixed solvent and additives according to a known method. be able to. The mixing and dispersing treatment can be carried out using a known mixing and dispersing machine such as a high-speed mixer, a homomixer, a ball mill, a roll mill, and an ultrasonic disperser. When two or more types of mixing and dispersing machines are used in combination, a good dispersion state can be easily obtained.

In preparing the electrically insulating resin composition, a dispersant such as a phosphate ester dispersant may be used. Dispersants may be used in embodiments where they are mixed together with the polyamideimide resin and silica particulates. In other embodiments, the dispersant may be used in a premixed form with the silica particulates prior to preparing the electrically insulating resin composition. The dispersant may not only adhere to the surface of the silica fine particles, but may also float in the system of the electrically insulating resin composition.

2. Electrical Insulator The electrically insulating resin composition of the above embodiment can be suitably used as an electrically insulating material for imparting insulation to various conductors. One embodiment relates to an electrical insulator having a conductor and an insulating film formed from the electrically insulating resin composition of the above embodiment for imparting insulation to the conductor. The above-mentioned insulating film can be formed, for example, by applying the electrically insulating resin composition of the above-described embodiment to a conductor and baking it.

Examples of the conductor include metal wires such as copper wires, and other structures that are desirable to have insulation properties. In the electrical insulator, the conductor may further have an additional insulating film made of another electrically insulating material in addition to the insulating film made of the electrically insulating resin composition.

(conductor)
Examples of the conductor include metal wires, which will be described later, and electrical and electronic components used in inverter-controlled electrical equipment and the like. Electrical and electronic components provided with an insulating film formed from the electrically insulating resin composition of the above embodiment are particularly useful for high voltage applications and inverter control applications.

Electrical and electronic components to which high voltage is applied and electrical and electronic components used in inverter-controlled electrical equipment tend to suffer from partial discharge deterioration of insulating films due to the rise in surge voltage values in recent years, and their withstand voltage life tends to be short. be. On the other hand, the insulating film formed from the electrically insulating resin composition of the above embodiment has excellent resistance to partial discharge deterioration, and therefore can be suitably used for surge countermeasures for electrical and electronic components.

When the electrical insulating resin composition of the above embodiment is applied to a metal wire, it meets typical performance requirements such as excellent resistance to partial discharge deterioration, processing resistance such as flexibility, heat resistance, and dielectric breakdown voltage characteristics. We can provide insulated wires (enamel wires) with high insulation reliability that satisfy the following requirements. Further, by using the insulated wire of the above embodiment, it is possible to provide an electrical/electronic component that has high resistance to dielectric breakdown and has an excellent withstand voltage life. In addition, dielectric breakdown due to partial discharge is not limited to the insulation coating of insulated wires, but also occurs in insulation films such as interphase insulation paper of electric motors, insulation varnish that coats motor coils, and electrical power equipment such as generators, transformers, and switchgears. Since this also occurs in insulating wires and filled molded insulating members, the electrically insulating resin composition of the above embodiment can also be used as an electrically insulating material for forming these insulating parts.

(Method for producing insulating film)
The method for applying the electrically insulating resin composition of the above embodiment is not particularly limited, and techniques well known in the art can be applied. For example, when applying an electrically insulating resin composition prepared as an electrically insulating paint (varnish) to an electric wire (metal wire), methods such as die coating and felt coating can be applied.

The electrically insulating resin composition of the above embodiment can form an insulating film by drying and curing the coating after being applied to a conductor to be coated. Drying and curing of the coating film can be achieved by heat treatment at a temperature of 260 to 520°C for a time of 2 seconds to several minutes. If the temperature during heat treatment is low, the solvent may remain after drying and curing of the coating film, which may deteriorate the coating properties. Furthermore, if the temperature during curing is not sufficiently high (for example, if the curing temperature is less than 260° C.), the drying and curing of the coating may be insufficient. If the heating time is too short, the solvent will remain in the coating film and the properties of the coating film will likely deteriorate. On the other hand, if the heating time is too long, time and energy are wasted and production efficiency tends to decrease.

The method of drying and curing (baking method) of the electrically insulating resin composition applied to the metal wire (electric wire) can be carried out according to a conventional method. A typical example is a method in which an electric wire is coated with an electrically insulating resin composition and then passed through a heating furnace. From the viewpoint of improving the dielectric breakdown resistance of the insulating film made of the cured film formed by the above-mentioned drying and curing, it is preferable to form the insulating film by repeating the application of the electrically insulating resin composition several times.

The insulating film may have a single layer structure or a multilayer structure. Although not particularly limited, in one embodiment, the total thickness of the insulating film is preferably 20 to 200 μm, more preferably 40 to 150 μm. If the coating is too thin, the insulation will be insufficient, and if it is too thick, the conductor ratio will decrease when it is made into a coil, resulting in a decrease in electrical performance. Moreover, if the coating film is too thick, it will be disadvantageous for miniaturization and thinning.

(Insulated wire (enamel wire))
Next, as an example of the electrical insulator, an insulated wire will be explained in more detail. FIG. 1 is a schematic cross-sectional view showing one embodiment of an insulated wire. 2 to 4 are schematic cross-sectional views showing other embodiments of the insulated wire. The insulated wire A shown in FIG. 1 includes a conductor 1 and an insulating film 2 formed by applying and baking the electrically insulating resin composition of the above embodiment onto the conductor 1.

A specific example of the conductor 1 is a metal wire such as a copper wire. In one embodiment, the cross-sectional shape of the metal wire may be circular, as shown in FIG. In other embodiments, the cross-sectional shape of the metal wire may be square, rectangular, or rectangular.

The insulating film 2 may have a multilayer structure in combination with other electrically insulating materials. In this case, the insulating film has a multilayer structure in which two or more layers of different electrically insulating materials are laminated. In such a multilayer structure, the insulating film formed from the electrically insulating resin composition of the above embodiment may be the innermost layer in contact with the conductor, the outermost layer in contact with the outside air, or the intermediate layer. There may be. Other electrically insulating materials include, for example, polyesterimide resins, polyurethane resins, polyester resins, polyimide resins, and polyamideimide resins that are essentially free of inorganic particles.

In one embodiment, the insulated wire A may have a structure including a primer layer 3 between the conductor 1 and the insulating film 2, as shown in FIG. In another embodiment, the insulated wire A may have a structure including a conductor 1, an insulating film 2, and an overcoat layer 4, as shown in FIG. Furthermore, in another embodiment, the insulated wire A may have a structure including a conductor 1, a primer layer 3, an insulating film 2, and an overcoat layer 4.

Although the primer layer and the overcoat layer are not particularly limited, from the viewpoint of resin compatibility with the insulating film 2, it is preferable that the primer layer and the overcoat layer are made of a polyamide-imide resin that essentially does not contain inorganic particles. Although the primer layer and the overcoat layer may contain less than 5 parts by mass of inorganic particles based on 100 parts by mass of the polyamide-imide resin, it is preferable that the primer layer and the overcoat layer are composed of only the polyamide-imide resin. The polyamide-imide resin used to form the primer layer may be the same as the specific polyamide-imide resin constituting the electrically insulating resin composition of the above embodiment, but there is no particular restriction, and other polyamides having a higher Mn may be used. Imide resins may also be used. For example, in one embodiment, the polyamideimide resin used to form the primer layer and overcoat layer may have an Mn of 23,000 to 29,000.

As described above, in the insulated wire A, the conductor 1 is coated with the insulating film 2 formed from the electrically insulating resin composition of the above embodiment, thereby improving processing resistance such as flexibility, adhesion, and heat resistance. , and dielectric breakdown voltage characteristics, resulting in high insulation reliability. Therefore, the insulated wire of the above embodiment can be suitably used for a stator or rotor coil. Such stators or rotors are installed in inverter drive motors and other high voltage drive motors. Examples of inverter-driven motors include hybrid vehicle motors, electric vehicle motors, hybrid diesel locomotive motors, electric motorcycle motors, elevator motors, and motors used in construction machinery.

The coil constructed using the insulated wire of the embodiment described above can provide high insulation reliability in the above-mentioned applications, and can realize longer lifespans of electrical equipment and motors. Such an effect is particularly effective in inverter control where a high voltage is applied. Furthermore, the electrically insulating resin composition can provide sufficient dielectric breakdown voltage characteristics even to a thin insulating film, and therefore can contribute to miniaturization and weight reduction of electrical equipment, motors, and the like.

Hereinafter, the present invention will be explained in detail with reference to Examples. However, the present invention is not limited to the embodiments described below, and various changes can be made without departing from the gist of the present invention.
<1> Preparation of polyamide-imide resin In a flask equipped with a thermometer, stirrer, and cooling tube, 192.1 g (1.00 mol) of trimellitic acid anhydride and 250.3 g (1.0 mol) of 4,4'-diphenylmethane diisocyanate were added. .00 mol) and 362.0 g of N-methyl-2-pyrrolidone were added. Next, the temperature of these mixtures is gradually raised to 130°C over about 6 hours in a dry nitrogen stream, taking care to avoid rapid bubbling of carbon dioxide gas generated by the reaction, and the temperature is further kept at 130°C for 4 hours. In this way, a polyamideimide resin solution was obtained. This polyamide-imide resin solution was diluted with N,N-dimethylacetamide (DMAC) and further kept at 200°C for 2 hours to prepare a polyamide-imide resin solution with a resin concentration (solid content) of 40%. . When the polyamideimide resin in the obtained solution was analyzed, the number average molecular weight was 21,000 and the acid value was 40 mgKOH/g.

The number average molecular weight and acid value of the polyamideimide resin were measured as follows.
(Number average molecular weight (Mn))
The conditions at the time of measurement are as follows.
GPC model: Hitachi L6000
Detector: Hitachi L4000 type UV
Wavelength: 270nm
Data processing machine: ATT 8
Column: Gelpack GL-S300MDT-5 (x2)
Column size: 8mmφ x 300mm
Solvent: DMF/THF = 1/1 (liter) + phosphoric acid 0.06M + lithium bromide 0.06M
Sample concentration: 5mg/1ml
Injection volume: 5μl
Pressure: 49kgf/cm ² (4.8×10 ⁶ Pa)
Flow rate: 1.0ml/min

(Acid value)
0.5g of polyamideimide resin was collected, 0.15g of 1,4-diazabicyclo[2,2,2]octane was added thereto, 60g of N-methyl-2-pyrrolidone and 1mL of ion-exchanged water were added, and the polyamide-imide resin Stir until the imide resin is completely dissolved. The solution thus obtained was titrated potentiometrically using a 0.05 mol/L ethanolic potassium hydroxide solution.

<2> Preparation of electrically insulating resin composition (Example 1)
100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 13.5 parts by mass of wet silica fine particle sol (wet silica sol) were heated at 60 to 70°C. An electrically insulating resin composition was obtained by mixing and dispersing for 1 hour. The wet silica sol contained 30.5% by mass of sol-gel silica having an average primary particle diameter of 11 nm, and the content of DMAC as a dispersion medium was 69.5% by mass.
In the obtained electrically insulating resin composition, the content of silica fine particles was 10% by mass based on the total mass of the solid components.

(Example 2)
An electrically insulating resin composition was prepared in the same manner as in Example 1, except that the amount of wet silica sol was changed. Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 21.4 parts by mass of wet silica sol were heated at 60 to 70°C for 1 hour. An electrically insulating resin composition was obtained by mixing and dispersing the mixture.
In the obtained electrically insulating resin composition, the content of silica fine particles was 15% by mass based on the total mass of the solid components.

(Example 3)
An electrically insulating resin composition was prepared in the same manner as in Example 1, except that the wet silica sol was changed to a dry silica fine particle sol (dry silica sol). Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 27.4 parts by mass of dry silica sol were heated at 60 to 70°C for 1 hour. An electrically insulating resin composition was obtained by mixing and dispersing the mixture. The dry silica sol contained 15.0% by mass of dry silica fine particles having an average primary particle diameter of 11 nm, and the content of N,N-dimethylacetamide as a dispersion medium was 85.0% by mass.
In the obtained electrically insulating resin composition, the content of silica fine particles was 10% by mass based on the total mass of the solid content.

(Example 4)
In preparing the electrically insulating resin composition of Example 3, an electrically insulating resin composition was prepared in the same manner as in Example 1, except that the amount of dry silica sol was changed. Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 43.5 parts by mass of dry silica sol were heated at 60 to 70°C for 1 hour. An electrically insulating resin composition was obtained by mixing and dispersing the mixture.
In the obtained electrically insulating resin composition, the content of silica fine particles was 15% by mass based on the total mass of the solid content.

(Comparative example 1)
DMAC was further added to the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) to prepare an electrically insulating resin composition that did not contain silica sol (silica fine particles) (solid content was adjusted to 37%). amount 34%).

(Comparative example 2)
An electrically insulating resin composition was prepared in the same manner as in Example 1, except that the amount of wet silica sol was changed. Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 6.4 parts by mass of wet silica sol were heated at 60 to 70°C for 1 hour. Mixing and dispersion treatment was carried out over a period of time to obtain an electrically insulating resin composition.
In the obtained electrically insulating resin composition, the content of silica fine particles was 5% by mass based on the total mass of the solid components.

(Comparative example 3)
An electrically insulating resin composition was prepared in the same manner as in Example 1, except that the amount of wet silica sol was changed. Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solid content to 37%) and 40.3 parts by mass of wet silica sol were heated at 60 to 70°C for 1 hour. An electrically insulating resin composition was obtained by mixing and dispersing the mixture.
In the obtained electrically insulating resin composition, the content of silica fine particles was 25% by mass based on the total mass of the solid content.

(Comparative example 4)
An electrically insulating resin composition was prepared in the same manner as in Example 1, except that the amount of wet silica sol was changed. Specifically, 100 parts by mass of the previously prepared polyamide-imide resin solution (DMAC was added to adjust the solids content to 37%) and 52 parts by mass of wet silica sol were mixed at 60 to 70°C for 1 hour. An electrically insulating resin composition was obtained by dispersion treatment.
In the obtained electrically insulating resin composition, the content of silica fine particles was 30% by mass based on the total mass of the solid content.

<3> Evaluation of electrically insulating resin composition <3-1> Varnish properties (1) Viscosity change rate over time (storage stability)
For the electrically insulating resin compositions (varnishes) of Examples 1 to 4 and Comparative Examples 1 to 4, the rate of viscosity change over time (%) before and after storage at 25 ° C. for 1 month was calculated according to the following procedure.
First, the viscosity of a polyamide-imide resin composition (varnish) was measured before storage. Next, a certain amount of the resin composition (varnish) was placed in a sealed container, and the sealed container was stored in a dryer set at 25° C. for one month, and then the viscosity was measured. From each measured value, the viscosity change rate over time was calculated according to the following (Formula 1).

(Formula 1)
Viscosity change rate over time (%) = (V2-V1)/V1×100

In Formula 1, "V1" represents the initial viscosity (Pa·s) measured before storage. "V2" represents the viscosity (Pa·s) measured after storage at 25° C. for one month. Each viscosity measurement was conducted in accordance with JIS C 2103 using a B-type rotational viscometer under conditions of 25° C., No. 3 rotor, and 30 rpm. Table 1 shows the values obtained by viscosity measurement.

From the viewpoint of storage stability, the rate of change in viscosity over time (%) is preferably the same as the rate of change in the case of not containing fine silica particles, or less than the rate of change above. The initial viscosity V1 (Pa·s) measured under the above conditions is preferably 2.3 or less, more preferably 2.1 or less, and even more preferably 2.0 or less. In such an initial viscosity range, the rate of change in viscosity over time (%) is preferably 24% or less.

(2) Turbidity (dispersibility)
Turbidity was determined according to the transmitted scattered light method. First, using a spectrocolorimeter "COH400" manufactured by Nippon Denshoku Kogyo Co., Ltd., the light intensity of the electrically insulating resin compositions of Examples 1 to 4 and Comparative Examples 1 to 4 was measured. The measurement conditions are as follows.
(Measurement condition)
Light source: tungsten lamp, color temperature 2500 degrees (absolute temperature)
Cell dimensions (total optical path length): 10cm
Acceptance angle for incident light: 90±30°
Peak sensitivity characteristic: 500nm
Next, turbidity was determined from the obtained values based on a calibration curve using a formazin standard solution. The results are shown in Table 1. The unit of turbidity is Nephelometric Turbidity Units (NTU). The smaller the turbidity value, the more transparent the electrically insulating resin composition is, and the better the dispersibility of the silica particles.

<3-2> Insulated wire characteristics (insulation film characteristics)
The electrical insulating resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were applied to a copper wire with a diameter of 1.0 mm, and then baked to obtain an insulated wire having an insulating film with a thickness of 0.034 mm. Manufactured.

The conditions for manufacturing the insulated wire and the method for measuring the thickness of the insulating film are as follows.
(Coating and baking conditions)
Baking furnace: Hot air type furnace (furnace length 5m)
Number of times of painting: 8 times of die drawing (painting and baking were repeated 8 times)
Furnace temperature: Inlet (evaporation zone)/Outlet (curing zone) = 320℃/430℃
Linear speed: 16m/min

(Measurement of insulation film thickness)
To determine the coating thickness of an insulated wire, measure the diameter (D1) of the insulated wire using a micrometer, then measure the diameter (D2) of the conductor after removing the coating by burning, and divide the difference by 1/2. I asked for it by making it .

Each characteristic of the insulating film in the obtained insulated wire was tested and evaluated by the following method. The results are shown in Table 1. In Table 1, the solid content of the varnish is a value calculated from the total amount of polyamideimide (PAI) resin and silica fine particles.

(1) Withstand voltage life characteristics (partial discharge deterioration resistance)
Using the previously produced insulated wires, a two-piece twisted sample as specified in JIS C3216-5 was prepared. Next, a rectangular wave alternating current voltage of 20 kHz was applied to this sample under conditions of a measurement temperature of 155±3° C. and a pulse voltage of 3000 V, and the time until dielectric breakdown of the sample occurred was measured.
If the withstand voltage life is 5 hours or more, it is within a practical range. The withstand voltage life is preferably 15 hours or more, more preferably 30 hours or more.

(2) Flexibility Measured according to JIS C3216-3. Table 1 shows the diameters at which no cracks were observed when the previously produced insulated wire was wound at 20% elongation and the insulating film was visually observed. If no cracks are observed at twice the diameter, it is within a practical range, and if it is three times the diameter or more, it is not practically desirable.

(3) Adhesion According to JIS C3216-3, the insulating film that had been left for one day or more after baking was twisted at a rotational speed of 100 times/min, and the rotational speed until the film peeled off was measured. If the number of rotations is 80 times or more, it is within a practical range, and if it is less than 80 times, it is not practically desirable.

(4) Softening resistance (heat resistance)
The measurement was carried out according to JIS C3216-6 using the previously prepared insulated wire. A softening temperature of 400°C or higher is within a practical range, and a softening temperature of less than 400°C is not practically desirable. The softening temperature is preferably 450°C or higher, more preferably 480°C or higher.

(5) Dielectric breakdown voltage characteristics Measurements were made according to JIS C3216-5 using the previously produced insulated wire. A dielectric breakdown voltage of 8 kV or more is within a practical range. The dielectric breakdown voltage is preferably 9 kV or more, more preferably 10 kV or more.

From the results shown in Table 1, the electrical insulating resin compositions obtained in Examples 1 to 4 achieved the flexibility required for the insulation film of the insulated wire by using a specific amount of silica fine particles. It can be seen that while adhesion, heat resistance, and dielectric breakdown voltage characteristics are maintained, partial discharge deterioration resistance is improved and excellent withstand voltage life characteristics are obtained. On the other hand, in Comparative Example 1, which does not contain silica fine particles, and Comparative Example 2, which has a small content of silica fine particles, the withstand voltage life characteristics are significantly reduced. In addition, in Comparative Examples 3 and 4, the content of silica fine particles was high, so the withstand voltage life characteristics were excellent, but the flexibility of the insulating film was reduced, and the storage stability was also significantly reduced. .

Furthermore, from a comparison between Examples 1 and 3 and Examples 2 and 4, even if the content of silica particles is the same, when wet silica particles (sol-gel silica particles) are used (Examples 1 and 2) In this case, the initial viscosity value was lower and the result was close to the time-dependent viscosity change rate value of Comparative Example 1 which did not contain silica fine particles. Further, the turbidity values when using sol-gel silica particles (Examples 1 and 2) are significantly smaller than when using dry silica particles (Examples 3 and 4). From this, it can be seen that even if the content is the same, by using wet silica fine particles, better dispersibility can be obtained and better withstand voltage life characteristics can be obtained.

As described above, according to the present invention, it is possible to provide an electrically insulating resin composition suitable as an electrically insulating material for forming an insulating film, and by using such an electrically insulating resin composition, it is possible to It is also possible to provide an electrical insulator with excellent withstand voltage and life characteristics. Therefore, the electrically insulating resin composition according to the present invention is particularly useful for improving the long-term reliability of inverter-driven motors, which are becoming increasingly high in frequency and voltage.

Claims (7)

A polyamide-imide resin containing silica fine particles having an average primary particle diameter of 50 nm or less , wherein the polyamide-imide resin has a number average molecular weight of 12,000 to 30,000 , and the silica particles are based on the total mass of the solid content. An electrically insulating resin composition having a fine particle content of 10 to 15 % by mass. The electrically insulating resin composition according to claim 1, wherein the silica particles include wet silica particles. The electrically insulating resin composition according to claim 1 or 2, having a turbidity of 30 NTU or less. The electrically insulating resin composition according to any one of claims 1 to 3, wherein the silica fine particles are a silica sol dispersed in a dispersion medium containing N,N-dimethylacetamide. The electrically insulating resin composition according to any one of claims 1 to 4 , wherein the polyamide-imide resin has an acid value of 30 to 50 mgKOH/g. An electrical insulator comprising a conductor and an insulating film formed using the electrically insulating resin composition according to any one of claims 1 to 5 . 7. The electrical insulator of claim 6 , wherein the conductor is a metal wire.

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